Multiple metals exposure and neurotoxic risk in bald eagles (Haliaeetus leucocephalus) from two Great Lakes states

Exposure to Sublethal Concentrations of Lead (Pb) Affects Ecologically Relevant Behaviors in House Sparrows (Passer domesticus)

Global contamination of environments with lead (Pb) poses threats to many ecosystems and populations. While exposure to Pb is toxic at high concentrations, recent literature has shown that lower concentrations can also cause sublethal, deleterious effects. However, there remains relatively little causal investigation of how exposure to lower concentrations of environmental Pb affects ecologically important behaviors. Behaviors often represent first-line responses of an organism and its internal physiological, molecular, and genetic responses to a changing environment. Hence, better understanding how behaviors are influenced by pollutants such as Pb generates crucial information on how species are coping with the effects of pollution more broadly. To better understand the effects of sublethal Pb on behavior, we chronically exposed adult wild-caught, captive house sparrows (Passer domesticus) to Pb-exposed drinking water and quantified a suite of behavioral outcomes: takeoff flight performance, activity in a novel environment, and in-hand struggling and breathing rate while being handled by an experimenter. Compared to controls (un-exposed drinking water), sparrows exposed to environmentally relevant concentrations of Pb exhibited decreases in takeoff flight performance and reduced movements in a novel environment following 9-10 weeks of exposure. We interpret this suite of results to be consistent with Pb influencing fundamental neuro-muscular abilities, making it more difficult for exposed birds to mount faster movements and activities. It is likely that suppression of takeoff flight and reduced movements would increase the predation risk of similar birds in the wild; hence, we also conclude that the effects we observed could influence fitness outcomes for individuals and populations altering ecological interactions within more naturalistic settings.

Lead, cadmium, and other trace elements in the liver of golden eagles and white-tailed eagles: recent data from Poland and a systematic review of previous studies

The golden eagle (Aquila chrysaetos) and the white-tailed eagle (Haliaeetus albicilla), being apex predators and facultative scavengers, can bioaccumulate different environmental contaminants, including toxic elements that may adversely affect their health. We analyzed the levels of cadmium (Cd), lead (Pb), and other metals and metalloids, including arsenic (As), barium (Ba), beryllium (Be), cobalt (Co), chromium (Cr), copper (Cu), iron (Fe), magnesium (Mg), manganese (Mn), molybdenum (Mo), selenium (Se), thorium (Th), thallium (Tl), uranium (U), vanadium (V), and zinc (Zn) in liver samples taken from three golden eagles and 36 white-tailed eagles that were found dead across Poland to verify their exposure. We also used a systematic review to summarize the available literature data on Cd, Pb, and other studied elements in the liver of both eagle species. Analyses of trace elements in the liver samples of the Polish eagles revealed interspecific differences in Cd, Cu, and Mn and differences in Co, Mn, Tl, and Zn among study regions. All elements tested except Pb were below the suggested thresholds linked with adverse health effects in birds. The hepatic Pb found in almost half of all the tested individuals suggests environmental exposure to this toxic element. One of the tested white-tailed eagles had hepatic Pb above the threshold of sublethal poisoning. Although our results seem optimistic, as previous Polish studies showed a higher prevalence of birds with hepatic Pb exceeding the toxicity threshold, they indicate that exposure to this toxic metal could still pose an additional threat to the health of Polish eagles.

Lead and Other Trace Element Levels in Brains of Croatian Large Terrestrial Carnivores: Influence of Biological and Ecological Factors

Trace element pollution can adversely affect the brains of individuals and thus impact the entire population of apex predators, such as large European carnivores. We assessed exposure to prominent neurotoxicants As, Cd, Hg and Pb by measuring their brain stem levels in brown bears (n = 114), grey wolves (n = 8), Eurasian lynx (n = 3), and golden jackals (n = 2) sampled in 2015-2022 in Croatia. The highest of the non-essential elements was the Pb level in the bears' brains (median, Q1-Q3; 11.1, 7.13-24.1 μg/kg wet mass), with 4% of animals, all subadults, exceeding the established normal bovine levels (100 μg/kg wet mass). Species-specific differences were noted for Ca, Cd, Cu, Fe, Pb and Se brain levels. Female brown bears had higher As brain levels than males. Cubs and yearlings had lower brain Cd, but higher Zn, while subadults had higher Cu than adult bears. Hepatic As, Cd, Cu and Hg levels were shown to be a moderate proxy for estimating brain levels in bears (r_S = 0.30-0.69). Multiple associations of As, Cd, Hg and Pb with essential elements pointed to a possible interaction and disturbance of brain Ca, Cu, Fe, Se and Zn homeostasis. Non-essential element levels in the brains of four studied species were lower than reported earlier for terrestrial meso-carnivores and humans. The age and sex of animals were highlighted as essential factors in interpreting brain element levels in ecotoxicological studies of large carnivores.

Mercury and neurochemical biomarkers in multiple brain regions of five Arctic marine mammals

Mercury is a neurotoxic chemical that represents one of the greatest pollution threats to Arctic ecosystem health. Evaluating the direct neurotoxic effects of mercury in free ranging wildlife is challenging, necessitating the use of neurochemical biomarkers to assess potential sub-clinical neurological changes. The objective of this study was to characterize the distribution and speciation of mercury, as well as exposure-associated changes in neurochemistry, across multiple brain regions (n = 10) and marine mammal species (n = 5) that each occupy a trophic niche in the Arctic ecosystem. We found consistent species differences in mean brain and brain region-specific concentrations of total mercury (THg) and methyl mercury (MeHg), with higher concentrations in toothed whales (narwhal, pilot whales and harbour porpoise) compared to fur-bearing mammals (polar bear and ringed seal). Mean THg (μg/g dw) in decreasing rank order was: pilot whale (11.9) > narwhal (7.7) > harbour porpoise (3.6) > polar bear (0.6) > ringed seal (0.2). The higher THg concentrations in toothed whales was associated with a marked reduction in the percentage of MeHg (<40 %) compared to polar bears (>70 %) that had lower brain THg concentrations. This pattern in mercury concentration and speciation corresponded broadly to an overall higher number of mercury-associated neurochemical biomarker correlations in toothed whales. Of the 226 correlations between mercury and neurochemical biomarkers across brain regions, we found 60 (27 %) meaningful relationships (r>0.60 or p < 0.10). We add to the growing weight of evidence that wildlife accumulate mercury in their brains and demonstrate that there is variance in accumulation across species as well as across distinct brain regions, and that some of these exposures may be associated with sub-clinical changes in neurochemistry.

Lead Intoxication in Free-Ranging Bald Eagles (Haliaeetus leucocephalus)

Lead toxicity due to ingestion of spent ammunition is an ongoing cause of mortality in bald eagles. While gross and histologic lesions of lead intoxication have been described in a few individuals of this species, the prevalence of lesions is underreported. A retrospective study of 93 bald eagles with severe lead intoxication was performed to describe the associated lesions and their prevalence and to compare the lesions with blood, liver, kidney, and/or bone lead concentrations. Gross lesions associated with lead toxicity were most frequent within the heart (51/93 birds) and consisted of multifocal myocardial pallor and rounding of the apex. Within the brain, gross lesions included petechiae or hemorrhagic necrosis (13/93 birds). Histologic lesions compatible with lead toxicity occurred within the heart (76/93 birds), brain (59/93 birds), and eyes (24/87 birds). Lead toxicity in bald eagles is characterized by fibrinoid necrosis of small- to medium-caliber arteries, most commonly affecting the heart, brain, and eyes. Gross and histologic lesions are consistent with ischemia caused by a primary vascular injury. A blood lead concentration of greater than 4 ppm and markedly elevated liver lead concentrations were associated with a greater likelihood of lesions in the heart. Severe lead intoxication is frequently associated with lesions that are histologically detectable in bald eagles. The presence of fibrinoid arterial necrosis and parenchymal degeneration, necrosis, and/or hemorrhage within the heart, brain, and/or eyes is suggestive of lead toxicity in bald eagles and warrants evaluation of liver or bone lead concentrations.

Concentrations of lead and other elements in the liver of the white-tailed eagle (Haliaeetus albicilla), a European flagship species, wintering in Eastern Poland

As a top predator, the white-tailed eagle (Haliaeetus albicilla) may serve as a good indicator species, providing information about the bioavailability of contaminants and their transfer within the food chain. In this study, we aimed to determine the common sources of origin of 17 metals and other elements in the liver of white-tailed eagles, and to compare the variations in their hepatic concentrations by age (adults vs immatures) and sex (males vs females) in groups of white-tailed eagles wintering in Eastern Poland. The element concentrations followed the pattern of S > K > Na > Fe > Mg > Ca > Zn > Cu > Mn > Se > Pb > Hg > Cd > Cr > Sr > V > Sc. We found significant age-related differences in the hepatic concentrations of some of the elements. Adults showed higher concentrations of Pb, Cd, Ca, Fe, and Zn and lower concentrations of Cu and Se than immatures. These differences may be explained by age-related differences in wintering strategy (adults are sedentary, and immatures are migratory) and hunting skills (adults are more successful when hunting for agile prey). Our study indicates that ingested Pb ammunition poses a serious threat to the health and lives of white-tailed eagles in Poland (32% of the studied individuals had acute lead poisoning). Our study also indicates a serious need for banning the use of lead hunting ammunition in the parts of Europe (including Poland) where it is still allowed.

Dietary mercury exposure causes decreased escape takeoff flight performance and increased molt rate in European starlings (Sturnus vulgaris)

Mercury is a widespread and persistent environmental contaminant that occurs in aquatic and terrestrial habitats. Recently, songbirds that forage from primarily terrestrial sources have shown evidence of bioaccumulation of mercury, but little research has assessed the effects of mercury on their health and fitness. There are many indications that mercury negatively affects neurological functioning, bioenergetics, and behavior through a variety of mechanisms and in a wide array of avian taxa. Effective flight is crucial to avian fitness and feather molt is an energetically expensive life history trait. Therefore, we investigated whether mercury exposure influenced flight performance and molt in a common songbird, the European starling (Sturnus vulgaris). Specifically, we dosed the diet of captive starlings with methylmercury cysteine at 0.0, 0.75, or 1.5 μg/g wet weight and recorded changes in flight performance after 1 year of dietary mercury exposure. We also recorded the annual molt of wing feathers. We found that individuals dosed with mercury exhibited decreased escape takeoff flight performance compared with controls and blood mercury was also correlated with an increased rate of molt, which can reduce flight performance and thermoregulatory ability. This study reveals two novel endpoints, flight performance and molt, that may be affected by dietary mercury exposure. These findings suggest a potential impact on wild songbirds exposed to mercury levels comparable to the high dosage levels in the present study. Any decrease in flight efficiency could reduce fitness due to a direct impact on survival during predation events or by decreased efficiency in other critical activities (such as foraging or migration) that require efficient flight.

Population declines and heavy metal exposure of Swinhoe's Storm Petrels (Oceanodroma monorhis) breeding on the southwest coast of Korea

We investigated the population dynamics of globally near-threatened Swinhoe's Storm Petrels on Kugul and Chilbal islets where >90% of the world breeding population have resided for >25 years. We also determined the levels of six heavy metals in the seabird species as a possible factor affecting reproduction. Of the 892 and 307 marked burrows since 1986, the breeding density of Swinhoe's Storm Petrels has changed significantly, based on a 55% decline at Kugul islet, and a 39% decline at Chilbal islet, suggesting that this species has suffered an extensive population decline. Of the individuals studied, five Swinhoe's Storm Petrels and two Streaked Shearwaters had >8.0 μg/g Pb in tissues, which is a potentially lethal level in avian species. Given that substantial changes in their breeding populations may occur in a limited breeding colony, ecological threats including environmental pollutants warrant attention for global conservation of these birds.